Classical Swine Fever

Description

Classical swine fever is a highly contagious, haemorrhagic disease of swine which is caused by a Togavirus. Presentation may be actue, sub-acute, chronic or persistent, and the disease is indistinguishable in the field from African Swine Fever. Acutely, classical swine fever is characterised by severe depression, high fever and superficial and internal haemorrhages, with many cases resulting in death. Depression, anorexia and pyrexia are seen in chronic classical swine fever. Transplacental infection is also possible and results in persistently infected piglets.

Aetiology

The Classical Swine Fever Virus is a Togavirus. Togaviruses belong to the genus Pestivirus, within the Flaviviridae family. The virus is enveloped, and has a positive-sense, single stranded RNA genome that is approximately 12.3kb long. Classical swine fever virus is closely related to the bovine viral diarrhoea virus of cattle, and the border disease virus of sheep.

Signalment

Domestic pigs and other swine of any age may become infected with classical swine fever.

Pathogenesis

Infection is by aerosol contact or direct spread. Entrance is through skin abrasions or mucous membranes. The incubation is usually 3-4 days (but may vary to 5-10 days). Virus infects epithelial cells of tonsillar crypts and subsequently spreads to regional lymph nodes via lymphatics. It enters the blood stream, replicates in the spleen, bone marrow and lymph nodes. Multiple haemorrhages are caused by degeneration of endothelial cells of blood vessles and thrombocytopaenia resulting in poor blood coagulation. In acute CSF, pigs die from the acute angiopathy, shock and febrile response. Pigs that survive develop a chronic form of the disease with enteric and joint lesions that are the result of tissue infarction. Piglets infected in utero are born persistently infected. They grow poorly and excrete virus over long periods.

Treatment

Control

• NOTIFIABLE disease
• Vaccination (live attenuated) in endemic countries:
  • Parts of EU are using vaccinated bait to control spread in wild boar population
  • Vaccination does not curtail spread: marker vaccine needed to distinguish virus exposure from vaccine-induced antibody